The large variety of hydrogen gas sensors are based on electronic devices and use of palladium as the active membrane. Reports on the most common hydrogen sensors of this type include: Palladium (Pd)-gated MOS transistors and Pd-gate metal-insulator-semiconductor (MIS) sensors (see K. I. Lundstrom, M. S. Shivaraman, C. M. Svensson. J. Appl. Phys. 46, 3876, 1975); Pd—CdS and Pd-insulator Schottky barrier diodes (see M. C. Steele and B. A. MacIver, Appl. Phys. Lett. 28, 687, 1976); the double metal-gate MISFET (see T. Yamamoto, and M. Morimoto, Appl. Phys. Lett., 20, 269, 1976) and the insulator gate field-effect transistor, IGFET, (see T. L. Poteat, and B. Lalevic, IEEE Trans. Electron Devices ED-29, 123, 1982); surface acoustic wave based sensors, SAW, (see A. D'Amico, A. Palma, and E. Verona, Appl. Phys. Lett. 41, 300, 1982); optical fiber sensors (see M. A. Buttler, Sensors and Actuators B 22, 155, 1994; A. Mandelis and J. A. Garcia, Sensors and Actuators B 49, 258, 1998; John W. Berthold, U.S. Pat. No. 6,519,041; Mendoza et al., U.S. Pat. No. 6,535,658; J. Mitsubishi, JP-2004-354, 163); optical interferometric sensor (see A. Bearzotti, C. Caliendo, E. Verona, and A. D'Amico, Sensors and Actuators B 7, 685, 1992), surface spectroscopic sensors (Eblen et al., U.S. Pat. No. 6,734,975); rare earth metal thin film sensors (Bhandari et al., U.S. Pat. No. 6,006,582; DiMeo et al., U.S. Pat. No. 6,596,236); electrochemical sensors (N. Taniguchi, US-2003/0024813; Kuriakose et al., US-RE38,344); catalytic sensors (Ito et al., U.S. Pat. No. 4,661,320); and photopyroelectric sensors (see A. Mandelis and C. Christofides, Sensors and Actuators B 2, 79, 1990; C. Christofides and A. Mandelis, Rev. Sci. Instr. 64, 3563, 1993).
Palladium (Pd) has proven to be a particularly suitable material due to its capability to absorb large amounts of hydrogen to form a hydride and to desorb reversibly. Taken together with polyvinylidene (di)fluoride (PVDF) as a photopyroelectric (PPE) sensor, it provides a way of detecting the presence of hydrogen due to the changes in electronic properties (pyroelectric coefficient of the OVDF and work function of Pd) and optical properties (surface absorptance and reflectivity), which result in a pyroelectric phenomenon that poled PVDF files (β phase) generates a voltage difference in the direction of poling between the two metalized electrode surfaces which sandwich the pyroelectric film when a temperature change is induced within the pyroelectric layer.
Previous work has focused on the fabrication of Pd-coated polyvinylidene (di)fluoride (Pd—PVDF) thin film photopyroelectric (PPE) sensors (see A. Mandelis and C. Christofides, Sensors and Actuators B 2, 79, 1990; C. Christofides and A. Mandelis, Rev. Sci. Instr. 64, 3563, 1993). A sensor that detected down to 0.075% hydrogen concentration in a flowing H2+N2 mixture by employing two detectors (one active and one reference) and two signal processing electronics (see A. Mandelis and C. Christofides, Sensors and Actuators B 2, 79, 1990). Since then efforts have been made to simplify the detection system by employing either a purely optical method (see A. Mandelis and J. A. Garcia, Sensors and Actuators B 49, 258, 1998) or by use of a single detector (see C. Christofides and A. Mandelis, Rev. Sci. Instrum. 64, 3563, 1993). However the detectivity in these cases was compromised by a large baseline signal and noise introduced by the intensity fluctuations of the incident light.
More recently a PPE interferometric sensor has been reported (see C. Wang, A. Mandelis and J. A. Garcia, Sensors and Actuators B 60, 228, 1999). In this case a He—Ne laser split into two beams and modulated out-of-phase with a mechanical chopper was used to generate the PPE signals. This system is bulky and not practical for portable hydrogen gas monitoring systems. There is a need for a device simpler in its hardware configuration and portable in deployment.